Transcript Unit 2: Chemical Reactions

Chemical
Reactions
What is a chemical reaction?
• A chemical reaction is the process by
which one or more substances undergo
change to produce one or more different
substances.
5 signs a chemical reaction has
taken place
1. Formation of gases or solids
2. Energy change (heat or electricity)
3. Color change
4. Odor change
5. Not easily reversed
Chemical Formulas
• A chemical formula is an abbreviation for a
chemical compound using chemical symbols
and numbers.
• The subscript number tells how many atoms of
the element are present in the compound
• Example: CO2 = Carbon Dioxide
– Di = 2
– 1 Carbon atom and 2 oxygen atoms
Chemical Equations
• Chemical equations use chemical symbols
to show the compound that is a result from
a chemical reaction
• Example: C + O2
CO2
– Carbon + 2 Oxygen = Carbon Dioxide
• Example: Na + Cl
NaCl
– Sodium + Chlorine = Sodium Chloride
Parts of a chemical equation
• The reactants in a chemical reaction are
the elements that combine to form a new
substance
• The products are the new compounds
Rules for chemical equations
• The total mass of the reactants must equal
the total mass of the products
• Equations must balance on both sides of
the equation
Chemical Compounds
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Ionic
Covalent
Acids
Bases
Salts
Covalent Compounds
• Result of a chemical reaction between
nonmetals
• DO NOT conduct electricity
• Have low melting points
Ionic Compounds
• A chemical reaction formed between a
metal and a nonmetal
• Conduct electricity
• Have high melting points
• Brittle – ions shift when hit, this causes
them to break apart
Acids
• A compound that increases the number of
hydrogen ions (H+) when dissolved in
water
• Acids react with metals producing
hydrogen gas
• Corrosive
• Conduct electricity
• Taste sour
• Found in batteries, your stomach, soft
drinks
Bases
• Any compound that produces hydroxide
ions (OH-) when dissolved in water
• Feels slippery
• Tastes bitter
• Conduct electricity
• Examples: soap, oven cleaners, drain
uncloggers, other cleaning products,
antacids
Salts
• An ionic compound formed from the
POSITIVE ion of a BASE and the
NEGATIVE ion of an ACID
• Example: Baking Soda – sodium
bicarbonate
– NaHCO3